# CVE-2026-98598: ipv6: Prevent rt6_insert_exception() for dying fib6_info. CVE-2026-98598 is fixed in 20 products on 1 platform, first by DEBIAN-CVE-2026-98598, released October 19, 2026. It is not reported as exploited. Patch Radar priority: Routine. - Web page: https://patchblox.com/security/cve/CVE-2026-98598 - Priority: Routine - CVSS: 4.1 (Moderate) - EPSS: 0.0020 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Oct 18, 2026 - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98598 ## Description In the Linux kernel, the following vulnerability has been resolved: ipv6: Prevent rt6_insert_exception() for dying fib6_info. Before the cited commit, fib6_nh_flush_exceptions() always set from->exception_bucket_flushed = 1 under rt6_exception_lock to prevent rt6_insert_exception() from inserting a new exception for a dying fib6_info. The flag was replaced with the FIB6_EXCEPTION_BUCKET_FLUSHED bit stored in nh->rt6i_exception_bucket. The problem is that now the bit is only set when the bucket is not NULL and fib6_nh_flush_exceptions() is called from fib6_nh_release() after fib6_ref has already reached zero. If rt6_insert_exception() is called while the target fib6_info is being removed via fib6_purge_rt(), a new exception could be created successfully because rt6_flush_exceptions() no longer sets the bit. This creates a reference cycle between the fib6_info and the exception route, leaking the fib6_info, its nexthop device, and all per-CPU routes in fib6_nh->rt6i_pcpu, which stalls netdev unregistration. [ 34.680602] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 [ 44.920675] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 [ 55.176582] unregister_netdevice: waiting for gre6 to become free. Usage count = 68 Let's call fib6_drop_pcpu_from() before rt6_flush_exceptions(), to set fib6_destroying before rt6_exception_lock, and check f6i->fib6_destroying in rt6_insert_exception(). Note that FIB6_EXCEPTION_BUCKET_FLUSHED logic is dead and we can clean it up in net-next. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | bpftool6.18 amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | bpftool6.18-debuginfo amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel-livepatch-6.18.56-125.164 amzn 2023 | 1:1.0-0.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18 amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18-debuginfo amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18-debuginfo-common-aarch64 amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18-debuginfo-common-x86_64 amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18-devel amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18-headers amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18-modules-extra amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18-modules-extra-common amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18-tools amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18-tools-debuginfo amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | kernel6.18-tools-devel amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | linux Debian 14 | 7.2.9-1 | [DEBIAN-CVE-2026-98598](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98598.md) | Oct 19, 2026 | | Linux | microvm-kernel6.18 amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | perf6.18 amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | perf6.18-debuginfo amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | python3-perf6.18 amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | | Linux | python3-perf6.18-debuginfo amzn 2023 | 1:6.18.56-125.164.amzn2023 | [ALAS2023-2026-3251](https://patchblox.com/security/data/fix/linux/alas2023-2026-3251.md) | Nov 7, 2026 | --- Data as of 2026-11-08T13:06:02Z UTC. 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